Hi David.
I know you're just getting started, but a couple of ideas came to mind with regard to a levelling type machine.
I guess you plan to have your router mounted into a sled type of affair, and being able to slide it across the the face, on the gantry rails. Good idea, just make sure those rails are substantial, against flex in either direction, particularly up and down.
How about gantry plates at each end, with slots, allowing you slide the Gantry up and down, and therefore set the required height manually. Build a spirit level into the gantry rails.
Really basic, but you could always motorise it later.
I know the trouble I've had in the past with regard to level the surface of an old table top. Something like this would have made my life a whole lot easier. However, you really do need to use it frequently to make it worthwhile.

Good Luck
Keep us posted on the build.

Gray

 

Well to keep it simple and positive I was initially thinking of creating an oblong frame with the aluminium, X axis, joined with a piece at each end, similar to what you already have designed. Short enough to fall between a pair of gantry plates similar to what you see on our Forum. And yes to could motorise it easily like that.
However, your rollers on your front to back lengths, ie, the Y axis, should each support a plate, its' height being, say the depth of your router plus whatever height you have in mind generally to level at, say up to 4" or 100mm depth.
Fit two bolts, long enough to go through each of the aluminium pieces across the ends of the X axis, and through the slotted plate with tightening knobs and a couple of washers on the ends.
To adjust the height just loosen of the knob, slide up or down the slot to the required height, at each side.

There you go. If that makes any sense.
Make sure you leave the ends open, and accessible, to be able to consider using it to level tables and doors, and many other applications.
I just read on a Woodworking Magazine Site, that a guy has made this incredible table top, but can't figure out how to level it off, it being sooo long.
You could make a much fancier one, and no doubt there will suggestions forthcoming on that point, but start simple, see if it works, and progress from there.

It has Great potential.
Go for it!
Gray